i've matched colorimetry on C100, GH3 and Nikon D800e. The key is to set all for post grading, having for example Neutral profile on GH3 all to minus 5, similar on D800e, shifting a bit hue, in camera. This way it's possible to get close look with the same kelvin setup (that's the point, dialing on different cameras different K, having similar picture, that grades after in you NLE. Do not have 5dmk3 on hands now, would imaging that approach should have similar results.